Marine vehicles, from large ships to umbilically controlled underwater robots (ROV's) and small submarines, typically use ducted propeller thrusters to control their position and attitude and, except for large ships and some submarines, to provide main propulsion. These thrusters can experience problems not limited to thrust-limiting cavitation at and near the surface, interruption of operations from ingestion of foreign objects, creating hazards to marine life and divers, and excessive screen resistance to flow.
What is needed is a system that addresses these problems while not reducing the thrust or efficiency of the thruster.